Implant Based Rehabilitation Options for the Atrophic Edentulous Jaw

Home , Alveolar process, Maxillary tuberosity

Australian Dental Journal The ofﬁcial journal of the Australian Dental Association Australian Dental Journal 2018; 63:(1 Suppl): S100–S107

doi: 10.1111/adj.12595

Implant based rehabilitation options for the atrophic edentulous jaw

KR Spencer

Melbourne Oral & Maxillofacial Surgeon, Melbourne, Victoria, Australia.

ABSTRACT The atrophic and edentulous jaw can pose a number of challenges for the implant clinician. In simple terms, the amount of bone that remains is insufﬁcient for the conventional placement of a dental implant. A variety of treatment strategies can be employed to enable implants to be placed despite the paucity of bone stock in either the mandible or the maxilla. Conceptually these strategies follow one of two pathways: either augmentation of the bone, or the novel utilization of the remaining bone. This article will discuss patient assessment, treatment planning, and the range of contemporary options available to enable ﬁxed implant based rehabilitation of each jaw. “The edentulous patient is an amputee, an oral invalid, to whom we should pay total respect and rehabilitation ambitions” (P-I Branemark, September 2005). Keywords: all on 4, alveolar atrophy, distraction osteogenesis, implant rehabilitation, mandibular grafting, maxillary grafting. Abbreviations and acronyms: CT = Computer tomography; OPG = Orthopantogram. Accepted for publication October 2017.

various medications including those taken for osteo- INTRODUCTION porosis can all reduce the success of both bone grafting and subsequent implant treatment. Anatomic changes in the atrophic jaw Clinical examination is undertaken to assess the As described and classified in the classical paper by intermaxillary relationship along with the health of Cawood and Howell,1 in a study of 300 dried skulls, the oral cavity and to exclude any pre-existing oral the alveolar process of the jaws undergo a progressive pathology. and predictable horizontal and vertical anatomical Measurement and photography of the resting verti- change following tooth loss. cal dimension of the face, along with the height of the Over time, the alveolar bone is completely resorbed smile needs to be documented in maxillary rehabilita- and even basal bone loss can occur as a result of over- tion cases in order to ensure that the transition zone loading from ill-fitting dentures (Fig. 1). between the oral mucosa and the prosthesis is hidden In the maxilla the bone loss can be so severe that under the upper lip. less than a millimetre of bone remains between the The use of cone beam CT scanning is essential in the oral cavity and nasal or sinus cavities, and in the treatment planning process as it allows the clinician to mandible the bone loss can result in exposure the infe- accurately visualise both the volume and configuration rior alveolar nerves (Fig. 2). of the residual bone (Fig. 3). In addition, in the max- Furthermore, with advanced atrophy, an unfavour- illa, it allows both the health and degree of pneumati- able Class III intermaxillary relationship develops sation of the sinus cavities to be assessed. In the mainly due to maxillary retrusion, this further compli- cates both ideal implant positioning and prosthetic rehabilitation.

PATIENT ASSESSMENT Patient history, examination and investigation are, as always, essential in treatment planning. Smoking, dia- betes, and a compromised immune system, along with Fig. 1 Extreme maxillary atrophy in a long-term denture wearer.

S100 © 2018 Australian Dental Association Implants in atrophic jaws mandible, it is an invaluable tool in preventing surgical sinus lift surgery and subsequent implantation. Nearly misadventure when it appears there is adequate bone 7000 implants were followed for 12–75 months with for implantation on an OPG (Fig. 4). an overall survival rate of 92.5%. The highest implant survival rate of 95.9% was reported with the use of non-autogenous grafting materials, compared to AUGMENTATION OF THE REMAINING MAXILLARY 87.7% for autogenous bone. BONE A graftless procedure where the void under the sinus membrane is ﬁlled with a blood clot that enables MAXILLARY REHABILITATION OPTIONS bone formation has also been described.3 Table 1. Maxillary rehabilitation options

Augmentation of the Utilization of the 2. Onlay bone graft remaining bone remaining bone Where there is a significant reduction in alveolar crest Sinus floor elevation Short implants width, bone can be grafted onto the anterior maxilla. + À / grafting Tuberosity implants If necessary, this can be done in combination with Onlay bone graft Pterygoid implants Le Fort 1 osteotomy “All-on-4â” sinus lifting. The bone can be sourced from a variety + bone graft Zygoma implants of local and regional sites, with the largest available reservoir being the hip (Fig. 6). A number of techniques have been described to aug- Depending on the clinical situation, implantation ment maxillary alveolar ridge width and height. In may be performed simultaneously or alternatively severe 3-dimensional atrophy, these techniques can be after the graft has healed. combined. A systematic review of this technique reported a mean survival rate of implants of 87.75%, however a relatively high rate of both donor (10%) and recipient 1. Sinus Floor elevation site complications (22%) were reported.4 The most Sinus floor elevation using the lateral window tech- significant of these complications occurs if the graft nique was first described by Tatum over 40 years ago. becomes exposed or infected, in which case there may In this technique, access to the maxillary sinus is be partial or total loss. obtained via a lateral bone window. The window is elevated and swung upwards and medially whilst 3. Le Fort I osteotomy being careful to ensure preservation of the sinus membrane (Fig. 5). In order to address the combination of both an unfa- A variety of materials can then be utilized to graft vourable intermaxillary relationship along with a lack the sinus floor including autogenous bone, alloplastic of bone stock, a Le Fort I osteotomy can be com- materials as well as carrier devices containing growth bined with interpositional bone grafting. The maxilla factors. If sufficient bone remains for primary stabil- is typically repositioned both forwards and down- ity, then implantation and grafting can be performed wards and the graft is secured to both the nasal and simultaneously. sinus floors. Although simultaneous grafting and Del Fabbro et al.2 performed a systematic review of implantation has been described, it is more commonly studies of over two thousand patients who underwent performed as a two-stage procedure. Due to the large

Fig. 2 Extreme mandibular atrophy with exposure of inferior alveolar nerves bilaterally.

Fig. 3 Cone beam CT of atrophic edentulous maxilla.

bridges. However, due to the complexity of the procedure a high incidence of complications in both the donor and recipient sites have also been reported.4

UTILIZATION OF THE REMAINING MAXILLARY BONE

Fig. 4 Cone beam slice reveals constriction of mandibular bone not 1. Short implants readily apparent when viewing from front on. Many early studies reported lower success rates with short implants, however with improvements in amount of bone graft required, the hip is always used implant surface technology, this is no longer the case. as the donor site. Finite element analysis (FEA) confirms that the Keller et al.5 were the first to describe the method maximum stress occurs along the top 5–6mmofan in combination with implant treatment in 1987. Nys- implant, and that implant diameter is more important trom et al.,6 followed 26 patients with 167 implants for stress distribution than length. for 11–16 years and reported an implant survival rate If there is adequate alveolar width and a minimum of 85%. At the end of the follow-up all the patients of 5 mm of bone remaining to the maxillary sinus, were still wearing their fixed implant supported the use of a short implant may avoid the need for S102 © 2018 Australian Dental Association Implants in atrophic jaws

anatomy, paying particular attention to the greater palatine artery, should perform implant placement in this region.

3. Pterygoid implants A pterygoid implant is anchored in the pterygoid plate of the sphenoid bone, through the maxillary and palatine bones with an angulation of between 35° and 55° and a length of 10–20 mm. In a review of studies reporting on a total of 1053 pterygoid implants in 676 patients, Candel et al.9 reported a success rate of 90.7%. Pterygoid implants may have an advantage over tuberosity implants as they engage dense cortical Fig. 5 Sinus ﬂoor elevation via lateral window and autogenous block bone, however they may be difﬁcult to restore due to graft. their posterior location, and the patient must have a minimum of 35 mm of mouth opening. Unfortunately the review article does not contain any information as to whether any of the implants studied were immediately loaded.

â 4. ‘All-on-4 ’ â Contemporary maxillary ‘All-on-4 ’ evolved from the original 1977 work of Branemark in which 4–6 verti- cally orientated implants were placed into the pre- maxilla, however in many cases this resulted in a too long distal cantilever. In order to overcome this problem, Matteson et al.10 in 1999, described a modifica- tion of the technique in which the posterior implants were placed at an angle parallel to the anterior wall of the maxillary sinus. Fig. 6 Multiple autogenous onlay block grafts in combination with tem- â porary implants used to support interim prosthesis during healing period. The concept of ‘All-on-4 ’ immediate function was developed by Malo et al.11 in 2003 and first applied to the mandible. Subsequently in 2005, he utilised the bone augmentation. Nisand and Renouard7 in 2014 same principle in the maxilla. reviewed multiple studies comparing short versus A recent comprehensive article by Chan and standard–length implants with various vertical aug- Holmes12 confirms the high success rate of the tech- mentation procedures and found similar survival rates. nique as reported by various independent authors However, the use of short implants resulted in a faster (95.2–100%) with follow up between 1–7 years. and lower-cost treatment with reduced morbidity. Currently this technique employs 4 implants: two They reported on 29 case series comprising 9780 straight anterior fixtures are combined with two distal short implants and found an overall cumulative sur- fixtures which are tilted posteriorly and, placed ante- vival rate of 96.67%. rior to the maxillary sinuses. The implants are inserted at a torque of >35 Ncm and are immediately restored. Implant placement can be performed via a 2. Tuberosity implants conventional open surgical procedure or alternatively If there is sufficient bone posterior to the sinus cavity, as a guided one by using the NobelClinicianTM Soft- an implant can be placed into the maxillary tuberos- ware and NobelGuideâ Surgical Template (Nobel ity. Lopez et al.8 reviewed studies following 113 Biocare AB, Zurich-Flughafen, Switzerland). patients with 289 implants and reported an overall An interesting variation of the standard technique survival rate over a period of 6–144 months of that shows promise, has been described by Jensen 94.63%. Due to the prevalence of Type III and IV et al.13 for use in those patients that have significant bone in this region, none of the studies reviewed mesial pneumatisation of the sinus cavities, but ade- reported immediate load or function of the fixtures. quate bone stock remaining anteriorly. In these cases An experienced surgeon with knowledge of the trans-sinus placement of the tilted implants in © 2018 Australian Dental Association S103 K Spencer

Fig. 7 Extra maxillary zygoma implant.

combination with bone morphogenetic protein 2 In an attempt to address this problem, Malo15 both grafting of the sinus floor was performed. Of the 19 redesigned the zygoma implant (by narrowing the tip trans-sinus implants placed, 18 remained integrated at and removing the coronal threads) and developed the the 1-year follow–up. This was presented as an alter- extramaxillary approach in which a channel is cut native treatment strategy to zygoma implants. along the lateral wall of the maxilla, the sinus mem- As maxillary atrophy progresses, there may be brane is preserved and elevated and the implant is â insufficient bone remaining for standard ‘All-on-4 ’ inset. By using this technique, the fixture head is posi- or any of its variants, and in these cases, zygoma tioned in a more prosthetically ideal position back implants may be required. towards the residual alveolar crest (Fig. 7). In recent review article by Chranovic et al.,16 4,556 zygoma implants were followed in 2,161 patients. 5. Zygoma implants The twelve-year cumulative survival rate was 95.21%, The use of long implants to engage the bone stock with most failures (103), occurring within the 6- within the zygoma was first described by Branemark14 month postsurgical period. Reported complications in in 1998. The original technique utilised bilateral order of prevalence were: sinusitis, soft tissue infec- zygoma implants in combination with four conven- tion, paraesthesia, and oro-antral fistula. tional dental implants in the anterior maxilla. The Following the principle that four implants provide technique has since undergone several modifications. enough support for a full arch fixed prosthesis, a mix- â â Following the ‘All-on-4 ’ concept, two zygoma fixture of ‘All-on-4 ’ and zygoma implants can placed. tures are now combined with two conventional implants, and in cases where there is insufficient anterior maxillary bone, four zygoma fixtures are placed â (quad zygoma). As with conventional ‘All-on-4 ’, the fixtures are placed into immediate function and the surgery can be performed as a conventional or guided procedure. Variations in zygoma placement surgery have been described. In the original Branemark technique, the fixtures entered the sinus cavity from a more palatal position. One of the criticisms of this method of placement was that the head of the fixture was placed too far towards the palate leading to a bulky prosthesis, which was difficult to clean. Fig. 8 Hybrid case ‘All-on-4’â and zygoma implants.

combinations of the two. The most common complications with onlay grafting are graft resorption and inci- sional dehiscence and graft exposure, and if this occurs some or all of the graft may be lost. Inlay grafting also has some limitations. It corrects only vertical, not horizontal defects, and the amount of vertical gain is anatomically limited to the stretch of the soft tissues attached to the superior bony segment.

2. Distraction osteogenesis First described in 1996,18 vertical distraction osteogenesis (VDO), can be applied to either the posterior or Fig. 9 Three zygoma implants placed to support an obturator in a total the anterior mandible. It may have advantages over maxillectomy patient. grafting procedures as there is no donor site morbidity and it may allow a greater vertical gain in bone height In this way, the surgeon can tailor the surgical proce- as the distraction process augments both hard and soft dure so the implants selected can make the most effi- tissues. In the atrophic edentulous mandible there is cient use of the available bone stock (Fig. 8). seldom enough bone remaining above the inferior The versatility of zygoma implants can also be alveolar nerve to allow for posterior distraction. Most demonstrated in a variety of other clinical scenarios. reported cases therefore discuss anterior distraction For example they can be used as a ‘rescue procedure’ where a horizontal osteotomy is performed anterior to when failure of one or more implants occurs in an the inferior alveolar nerves. A distraction device is â ‘All-on-4 ’. In these cases the failed implant removal secured to the bone and after a latency period of and the zygoma implant placement occur simultane- 7 days, the superior bone block (transport segment) is ously. The zygoma implant is placed into immediate then distracted by up to 1 mm per day. function as it is integrated into the existing fixed pros- From a review of the literature there appears to be thesis, thus avoiding the need for the patient to wear an unacceptably high rate of reported complications 19 an interim removable denture. (43.2–79.31%). These include breakage of distrac- Zygoma implants may also be utilised to stabilise tion device, fracture of the transport segment or an obturator in post -maxillectomy cancer patients mandible, inferior alveolar nerve injury, and lingual where the resultant defect and distorted anatomy tilting of the transport segment. Survival rates for make the wearing of a prosthesis difficult (Fig. 9). implants placed into distracted bone are similar to those reported for cases using other methods to augment the bone. MANDIBULAR REHABILITATION OPTIONS

Table 2. Mandibular rehabilitation options UTILISATION OF THE REMAINING BONE

Augmentation of the Utilization of the remaining bone remaining bone 1. Short implants

Bone grafting Short implants For atrophic mandibles, it is the posterior segment Distraction osteogenesis Nerve repositioning distal to the mental foramen that poses the greatest â “All-on-4 ” challenge. The rationale for placing a short implant in this region is to avoid the need for additional surgical procedures and their associated risks and additional cost. At the site of implantation there must be ade- AUGMENTATION OF THE REMAINING BONE quate width, and the residual bone height above the nerve canal needs to be at least 8 mm (6 mm 1. Bone grafting implant + 2 mm safety zone). Block17 provides an excellent description of both the history and the variety of procedures that can be per- 2. Nerve repositioning formed to augment the atrophic mandible. Either onlay grafting or inlay ‘sandwich’ bone graft- Nerve repositioning is one of the methods available to ing can be performed. Grafts include corticocancellous allow implant placement in the posterior mandible of blocks placed via intra or extra oral incisions, particu- patients who do not have sufﬁcient bone height above late material with membrane coverage, or the nerve for conventional implant placement. © 2018 Australian Dental Association S105 K Spencer

and multiple studies have shown both excellent long- term prosthetic and implant survival rates, along with high levels of patient satisfaction.22

DISCUSSION The ultimate goal of implant placement is to generate long-lasting anchorage in the best possible position for a functionally and aesthetically optimal prosthetic solution.23 However, implant placement in atrophic ‘ â’ Fig. 10 Standard mandibular All-on-4 . edentulous jaws can pose a significant treatment challenge, as there is often both a lack of bone, and an It may be performed by either lateralization or unfavourable anatomy of the bone that remains. The transposition. In lateralization the nerve is exposed clinician should be aware of the outcomes of different and retracted laterally during implant placement, then treatment options in order to be able to critically released to rest against the implants. In transposition, assess the best option for each clinical situation. A the mental foramen is included in the osteotomy, to variety of different treatment strategies have been pre- allow the nerve to be pulled into a completely new, sented for use in those patients seeking a fixed more posterior position. implant based solution. Over the last decade, patient Vetromilla et al.20 reviewed studies reporting on driven demand for an immediate single stage treat- both methods of nerve repositioning. Permanent neu- ment with low morbidity has seen a significant â rosensory disturbance was noted in 3.4% of patients increase in ‘graftless’ procedures such as ‘All-on-4 ’, who underwent lateralisation, and 22.1% of patients and now longer term data is available in the literature who underwent transposition. The use of Piezoelectric to support the validity of these approaches. There is devices may lead to a lower risk of injury, as com- also good long-term clinical data supporting the use pared to standard rotary devices, however this of shorter implants as well as traditional grafting pro- requires further study. cedures such as sinus lifting and onlay grafting. How- The success rate of the lateralisation regarding ever, due to the high reported complication rates, implant osseointegration was reported to be between nerve repositioning and distraction osteogenesis can- 93.8% and 100%. not be recommended.

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